§ 261. THE CEPHALOPODA. 299 



of these halves is also divided, and so on, forming four, eight, &c., segments, 

 each resembling a more and more acute triangle, with a converging apex, 

 while its base is directly continuous with the remaining vitellus. After a 

 certain number of segments have been formed by these longitudinal divisions, 

 transverse furrows are seen separating the apices of the segments, and 

 forming, at first, in the centre of the eminence, a ring composed of eight to 

 sixteen portions ; but finally, from a further segmentation in both direc- 

 tions, these furrows become a mass of increasingly smaller and more 

 numerous parts. ^^^ 



This portion of the vitellus, which, during this time, has also been devel- 

 oped at its periphery, is changed into a blastoderma composed of two layers. 

 Upon this blastodermal membrane several folds appear, which are the fii-st 

 traces of the future embryo, viz: first, a median, uneven fold or rudiment 

 of the mantle, and then two others, lateral, which ultimately form the eyes. 

 Between these three folds are placed two others which become the two lat- 

 eral halves of the funnel. Subsequently, the folds of the branchiae and arms 

 appear ; and among these last the two belonging to the ventral surface are 

 first seen. Still later, the folds of the eyes and arms, and their surrounding 

 parts, become more and more prominent upon the vitelline mass, thus 

 forming the cephalic portion of the embryo. From this last, opposite the 

 vitellus, the fold of the mantle is sketched as the future posterior portion of 

 the body. The general form of the animal may, therefore, be recognized 

 very early, although the cephalic portion quite exceeds that of the mantle. 



At the posterior or dorsal surface of the cephalic portion, the mouth 

 appears, first as a semilunar depression, and the internal layer of the blas- 

 toderma gradually extends from the border of this portion over the whole 

 vitelline mass, producing, finally, a ti'ue vitelline sac. The external surface 

 of this is covered with ciliated epithelium which gradually spreads over the 

 other parts of the embryo, such as the lobes of the head, the arms, the eyes, 

 and the mantle, while that of the branchiae, and the funnel, the halves of 

 which have then united, is never ciliated.® 



Of the Cartilages, the articular and cephalic are the first developed. The 

 internal shell,'** the nervous system, the heart with the vascular and respi- 

 ratory systems, the digestive canal and its appendages, and the ink-sac, are 

 formed successively, and may be easily seen at the termination of the 

 embrj^onic life, when, also, are found some chromatic cells. 



As to the vitelline sac, it should be remarked that it never communicates 

 with the intestinal canal, as has hitherto been supposed.''* The cephalic 

 portion, which always extends upon this sac, embraces a part of it, so that 

 it is divided by a constriction into an internal and external portion, the 

 former of which extends even into the cavity of the mantle. The con- 

 stricted portion is gradually elongated, and finally becomes a long, very 

 narrow canal, extending from the cephalic extremity to the side of the 



2 See Kollil-er, loc. cit. p. 17, Taf. I. p. 379, and Maravigno, Ann. d. Sc. Nat. VIL 



3 With Loligo, the vitelline sac and its ciliated 1837, p. 174. 



epithelium are formed quite early ; while with Se- 5 Most of the earlier anatomists were led into 



pia, they do not appear until the embryo and its error from the tenuity of the canal of communica- 



different organs have become quite large. With tion, and the difficulty of its examination. They 



the first, the embryos have rotatory movements, but supposed that the external vitelline sac communi- 



with the second this is not the case {Kolliker, loc. cated with the oesophagus and stomach, by this 



cit. p. 51). canal ; see Carus, loc. cit. Taf. II. fig. 27 (LoH- 



4 With Argonauta, the external shell is formed go) ; Cuvier, loc. cit. PI. VIII. fig. 9 ; Dugis, loc. 

 while the embryo after its escape from the egg, is cit. PI. V. fig. 3 (Sepia) and Van Beneden, \oc. cit. 

 still persistent ia the spawn inside the shell of its PI. I. fig. 13 {Sepiola). KoUiker was the first to 

 parent ; see Power, in Wiegmann's Arch. 1845, 1, view it correctly (loc. cit. p. 86, Taf. IV.). 



